The present invention relates to a chemical amplifying type positive resist composition used in the minute processing of a semiconductor.
A lithography process using a resist composition has usually been adopted in the minute processing of a semiconductor. In the lithography, the resolution can be improved with a decrease in wavelength of exposure light in principle as expressed by the equation of Rayleigh""s diffraction limit. A g-line with a wavelength of 436 nm, an i-line with a wavelength of 365 nm, and a KrF excimer laser with a wavelength of 248 nm have been adopted as exposure light sources for lithography used in the manufacture of a semiconductor. Thus, the wavelength has become shorter year by year. An ArF excimer laser having a wavelength of 193 nm is considered to be promising as a next-generation exposure light source.
A lens used in an ArF excimer laser exposure machine has a shorter lifetime as compared with lenses for conventional exposure light sources. Accordingly, the shorter time required or exposure to ArF excimer laser light is desirable. For this reason, it is necessary to enhance the sensitivity of a resist. Consequently, there has been used a so-called chemical amplifying type resist, which utilizes the catalytic action of an acid generated by exposure and contains a resin having a group cleavable by the acid.
It is known that, desirably, resins used in a resist for ArF excimer laser exposure have no aromatic ring in order to ensure the transmittance of the resist, but have an alicyclic ring in place of an aromatic ring In order to impart a dry etching resistance thereto. Various kinds of resins such as those described in Journal of Photopolymer Science and Technology, Vol. 9, No. 3, pages 387-398 (1996) by D. C. Hofer, are heretofore known as such resins.
As a resin used in a resist for ArF excimer laser exposure, a mutual copolymer composed of a polymerization unit of alicyclic olefin and a polymerization unit of an unsaturated dicarboxylic acid anhydride (T. I. Wallow et al., Proc. SPIE, vol. 2724, pp. 355-364 (1996)), a polymer having an alicyclic lactone structure unit (JP-A-2000-26446) and the like are known.
Conventionally, glycol ether esters, esters, ketones, cyclic esters and the like have been used as resist solvents. However, there is a problem that the solubility of the resins prepared by using a polymer having an alicyclic lactone structure unit In the conventional solvents is not satisfactory.
One object of the present invention is to provide a chemical amplification type positive resist composition comprising a resin component prepared by using a polymer having an alicyclic lactone structure unit and an acid generating agent which is particularly suitable for lithography using excimer lasers such as ArF and KrF, and has an excellent polymer dissolving capability.
The present inventers have conducted an extensive studies and have found that a solubility of the resin can be improved by using a specific amount of a specific solvent. The present invention has been accomplished based on this finding.
The present invention provides a resist composition comprising a resin having a alicyclic lactone structure unit that is insoluble in alkali by itself but becomes soluble due to the action of an acid, a solvent containing 2-heptanone and an acid generating agent, wherein a content of 2-heptanone in the solvent is in a weight ratio of from about 5 to about 95%.
Generally, a resist solution is prepared by dissolving each of the components consisting of a resin and an acid generating agent in a solvent, and the resist solution is then applied on a substrate such as a silicon wafer by a conventional method such as a spin coating. The solvent is required to dissolve each of the components, to attain a satisfactory drying rate and to supply an even and smooth coating after it is evaporated.
The resist composition of the present invention is characterized in that it contains 2-heptanoen as the specific solvent component, and a content of 2-heptanone in the solvent is in a weight-ratio of from about 5 to about 95%.
Other solvents such as esters, glycol ether esters, cyclic esters, ketones and the like may preferably be used since they will contribute to improve profiles Specific examples of the solvents include:
ethyl cellosolve acetate,
methyl cellosolve acetate,
propylene glycol monomethyl ether acetate,
methyl lactate,
butyl acetate,
amyl acetate,
ethyl pyruvate,
acetone,
methyl isobutyl ketone,
cyclohexanone and
ā-butylolactone,
As a specific example of a combination and a ratio of the above solvents, a combination of 2-heptanone and propylene glycol monomethyl ether acetate in a ratio of 5-95 wt. %:95-5 wt. % is preferable, since excellent dissolving properties as well as profile are expected by the combination.
It is also preferable to use a combination of 2-heptanone, propylene glycol monomethyl ether acetate and ā-butylolactone in a ratio of 10-85 wt. %:85-10 wt. %:1-10 wt. %, more preferably 19-75 wt. %:80-24 wt. %:1-10 wt. %, since excellent dissolving capability is expected.
The resin as a component of the positive resist composition of the present invention has an alicyclic lactone structure unit. The alicyclic lactone structure unit may preferably be selected from the group consisting of polymerization units represented by the following formulas (Ia) and (Ib) 
wherein R1, R2, R3 and R4 each independently represent hydrogen or methyl, n represents an integer of 1-3, provided that when R2 or R4 is two or more, each of them may be same as or different from each other.
Specific examples of a monomer from which the polymerization units represented by the formulas (Ia) and (Ib) are derived include (meth)acrylic acid esters of alicyclic lactone having a hydroxyl group shown below and mixtures thereof, such as those shown below. 
These esters can be prepared, for example by reacting a corresponding cyclic lactone having hydroxyl group with (meth)acrylic acids (e.g. JP2000-26446A).
The resin of the positive resist composition of the present invention is insoluble in alkali by itself but becomes soluble due to the action of an acid. Such a resin preferably contains a polymerization unit having a group de-blocked due to the action of an acid and becomes alkali-soluble due to the de-blockage is exemplified as the resin of the present invention.
Specific examples of the group de-blocked due to the action of an acid include various types of carboxylic acid esters, including: alkyl esters having about 1 to 6 carbons typified by tert-butyl ester: acetal esters such as methoxymethylester, ethoxymethylester, 1-ethoxyethyl ester, 1-isobutoxyethyl ester, 1-isopropoxyethyl ester, 1-ethoxypropyl ester, 1-(2-methoxyethoxy)ethyl ester, 1-(2-acetoxyethoxy)ethyl ester, 1-[2-(1-adamantyloxy)ethoxy]ethyl ester, 1-[2-(1-adamantanecarbonyloxy)ethoxy]ethyl ester, tetrahydro-2-furyl ester and tetrahydro-2-pyranyl ester, and alicyclic esters such as 2-alkyl-2-adamantyl, 1-(1-adamantyl)-1-alkylalkyl and isobornyl ester.
The monomer from which the polymerization unit having a carboxylic acid ester described above is derived may be an acrylic one such as methacrylic acid ester and acrylic acid ester, or an alicyclic monomer with a carboxylic ester group bound thereto, such as norbornene carboxylic acid ester. tricyclodecene carboxylic acid ester and tetracyclodecene carboxylic acid ester. Otherwise, it may be an ester formed by an alicyclic group of an alicyclic carboxylic acid ester and an acrylic acid or a methacrylic acid, as described in Iwasa et al., Journal of Photopolymer Science and Technology, Vol. 9, No. 3, pp. 447-456 (1996).
Among the monomers described above, one having a bulky group containing an alicyclic group such as 2-alkyl-2-adamantyl and1-(1-adamantyl)-1-alkylalkyl, as the group de-blocked due to the action of an acid, is preferably used because such a monomer exhibits excellent resolution. Examples of the monomer having a bulky group containing an alicyclic group include (meth)acrylic acid 2-alkyl-2-adamantyl, (meth)acrylic acid 1-(1-adamantyl)-1-alkylalkyl, 5-norbornene-2-carboxylic acid 2-alkyl-2-adamantyl and 5-norbornene-2-carboxylic acid 1-(1-adamantyl)-1-alkylalkyl.
Among others, use of (meth)acrylic acid 2-alkyl-2-adamantyl as the monomer is preferred for its excellent resolution. Typical examples of the (meth)acrylic acid 2-alkyl-2-adamantyl include acrylic acid 2-methyl-2-adamantyl, methacrylic acid 2-methyl-2-adamantyl, acrylic acid 2-ethyl-2-adamantyl, methacrylic acid 2-ethyl-2-adamantyl and acrylic acid 2-n butyl-2-adamantyl. Particularly, methacrylic acid 2-ethyl-2-adamantyl are preferred, since it gives good balance between sensitivity and heat resistance.
The resin to be used in the present invention can contain other polymerization unit(s), if required, in addition to the polymerization units represented by the formulas (Ia) and (Ib) and a polymerization unit having a group de-blocked due to the action of an acid.
Examples of the other polymerization units include a polymerization unit represented by the following formula (II), a polymerization unit derived from a polymerization unit represented by the following formula (III) and unsaturated dicarboxylic acid anhydride selected from maleic anhydride and itaconic anhydride, and a polymerization unit represented by the following formula (IV) and a polymerization unit represented by the following formula (V) and the like. 
wherein, R3, R7, R6 independently represent hydrogen or methyl, R4 represents hydrogen or a hydroxyl group. R5 and R6 independently represent hydrogen, alkyl group having 1 to 3 carbon atoms, hydroxyalkyyl group having 1 to 3 carbon atoms, carboxyl, cyano or group-COOR9 wherein, R9 is an alcohol residue, or R5 and R6 may be combined to form a carboxylic anhydride residue represented by xe2x80x94C(xe2x95x90O)OC(xe2x95x90O)xe2x80x94.
A monomer from which the polymerization unit represented by the formula (II) having (meth)acrylic acid 1-adamantyl-3-hydroxy is derived can be prepared by reacting a corresponding hydroxyadamantan with (meth)acrylic acids (e.g. JP63-33350A), for example.
Examples thereof Include:
3-hydroxy-1-adamantyl acrylate;
3-hydroxy-1-adamantyl methacrylate;
3,5-dihydroxy-1-adamantyl acrylate; and
3,5-dihydroxy-1-adamantyl methacrylate.
In the formula (III), R5 and R6 independently represent hydrogen, alkyl group having 1 to 3 carbon atoms, hydroxyalkyl group having 1 to 3 carbon atoms, carboxyl, cyano or group-COOR9, wherein R9 is an alcohol residue. R5 and R6 may be combined to form a carboxylic anhydride residue represented by xe2x80x94C(xe2x95x90O)OC(xe2x95x90O)xe2x80x94.
Specific examples of the alkyl group, as R5 or R6, include methyl, ethyl, propyl and the like. Specific examples of the hydroxyalkyl group(s), as R5 or R6, include hydroxymethyl, 2-hydroxyethyl and the like.
The group represented by xe2x80x94COOR9 is a esterified carboxyl. Examples of the alcohol residue as R9 include alkyl group having about 1 to 8 carbon atoms, which may optionally be substituted, 2-oxo-oxolane-3- or -4-yl and the like, wherein examples of the substituent for alkyl may be a hydroxyl group or an alicyclic hydrocarbon residue and the like.
Specific examples of the carboxylic acid ester residue(s) represented by xe2x80x94COOR9 include methoxycarbonyl, ethoxycarbonyl, 2-hydroxyethoxycarbonyl, tert-butoxycarbonyl, 2-oxo-oxolane-3-yloxycarbonyl, 2-oxo-oxolane-4-yloxycarbonyl, 1,1,2-trimethylpropoxycarbonyl. 1-cyclohexyl-1-methylethoxycarbonyl, 1-(4-methylcyclohexyl)-1-methylethoxycarbonyl, 1-(1-adamantyl)-1-methylethoxycarbonyl and the like .
Specific examples of monomers deriving an alicyclic polymerization unit represented by the formula (III) include:
2-norbornen;
2-hydroxy-5-norbornen;
5-norbornen-2-carboxylate;
methyl 5-norbornen-2-carboxylate;
5-norbornen-2-carboxylate-t-butyl
1-cyclohexyl-1-methylethyl 5-norbornen-2-carboxylate;
1-(4-methylcyclohexyl)-1-methylethyl
5-norbornen-2-carboxylate;
1-(4-hydroxycyclohexyl)-1-methylethyl
5-norbornen-2-carboxylate;
1-methyl-1-(4-oxocyclohexyl)ethyl
5-norbornen-2-carboxylate;
1-(1-adamantyl)-1-methylethyl 5-norbornen-2-carboxylate;
1-methylcyclohexyl 5-norbornen-2-carboxylate;
2-methyl-2-adamantyl 5-norbornen-2-carboxylate;
2-ethyl-2-adamantyl 5-norbornen-2-carboxylate;
2-hydroxy-1-ethyl 5-norbornen-2-carboxylate;
5-norbornen-2-methanol;
5-norbornen-2, 3-dicarboxylic acid anhydride;
The polymerization unit derived from the unsaturated dicarboxylic acid anhydride is selected from the group consisting of a polymerization unit derived from maleic anhydride and a polymerization unit derived from itaconic anhydride, which can respectively be represented by the following formulas (VI) and (VII).
Specific examples of a monomer to be used for deriving these polymerization units may be maleic anhydride, itaconic anhydride and the like. 
Specific examples of a monomer from which the polymerization unit of (meth)acrylic acid (xcex1)xcex2-xcex3-butylolactone represented by the formula (IV) is derived may be the following compounds that can be prepared by, for example. reacting hydroxy (xcex1) xcex2-xcex3-butylolactone with (meth) acrylic acids:
acrylic acid xcex1-xcex3-butylolactone,
methacrylic acid xcex1-xcex3-butylolactone,
acrylic acid xcex2-xcex3-butylolactone,
methacrylic acid xcex2-xcex3-butylolactone and the like.
Specific examples of a monomer from which the polymerization unit of the formula (V) is derived may be the following compounds:
acrylonitrile, and
methacrylonitrile.
Ratios of the polymerization units of the resin to be used in the present invention may be varied depending on a type of radiations for irradiation on patterning exposure, types of arbitrarily selected other optional polymerization units and the like. The ratio of the alicyclic lactone structure unit to the polymerization unit that will become soluble in an alkaline medium due to partial cleavage of the groups by the interaction of acid may preferably be about 90-20 wt. %:10-80 wt. %.
It is preferable to use from about 0.1 to about 50 parts by mol of the other polymerization unit in combination with the above polymerization units with respect to the total amount of the above polymerization units (100 parts by mol).
The copolymerized portion of the alicyclic olefin from which the unit of the formula (III) is derived and the unsaturated dicarboxylic acid anhydride selected from maleic anhydride and itaconic anhydride usually fores an alternating copolymer.
Copolymerization of the resin in the present invention can be conducted in accordance with conventional methods. For example, the copolymer resin of the present invention is obtainable by dissolving predetermined amount of monomers into a necessary amount of organic solvent, and then subjecting the solution to a polymerization reaction in the presence of a polymerization initiator such as azo compound including 2,2xe2x80x2-azobisisobutyronitrile, dimethyl 2,2xe2x80x2-azobis (2-methylpropionate). After the reaction, it is advantageous to purify the resin by way of reprecipitation or the like.
The acid generating agent, another component of the resist composition, is a substance which is decomposed to generate an acid by applying a radiation such as a light, an electron beam or the like on the substance itself or on a resist composition containing the substance. The acid generated from the acid generating agent acts on said resin resulting in cleavage of the group cleavable by the action of an acid existing in the resin.
Such acid generating agents, for example, include other onium salt compounds, organo-halogen compound, sulfone compounds, sulfonate compounds, and the like.
Specific examples thereof include:
diphenyliodonium trifluoromethanesulfonate,
4-methoxyphenylphenyliodonium hexafluoroantimonate,
4-mthoxyphenylphenyliodonium trifluoromethanesulfonate,
bis(4-tert-butylphenyl)iodonium tetrafluoroborate,
bis (4-tert -butylphenyl) iodonium hexafluorophosphate,
bis(4-tert-butylphenyl)iodonium hexafluoroantimonater
bis(4-tert -butylphenyl) iodonium trifluoromethanesulfonate,
triphenylsultfonium hexafluorophosphate,
triphenylsulfonium hexafluoroantimonate,
triphenylsulfonium trifluoromethanesulfonate,
4-methoxyphenyldiphenylsulfonium hexafluoroantimonate,
4-methoxyphenyldiphenylsulfonium
trifluoromethanesulfonate,
p-tolyldiphenylsulfonium trifluoromethanesulfonate,
p-tolyldiphenylsulfonium perfluorobutanesulfonate,
p-tolyldiphenylsulfonium perfluorooctanesulfonate,
2,4,6-trimethylphenyldiphenylsulfonium trifluoromethanesulfonate,
4-tert-butylphenyldiphenylsulfonium trifluoromethanesulfonate,
4-phenylthiophenyldiphenylsulfonium hexafluorophosphate
4-phenylthiophenyldiphenylsulfonium hexafluoroantimonate,
1-(2-naphthoylmethyl)thiolanium hexafluoroantimonate,
1-(2-naphthoylmethyl) thiolanium trifluoromethanesulfonate,
4-hydroxy-1-naphthyldimethylsulfonium hexafluoroantimonate,
4-hydroxy-1-naphthyldimethylsulfonium trifluoromethanesulfonate,
oyclohexylmethyl(2-oxocyclohexyl)sulfonium trifluoromethanesulfonate,
cyclohexylmethyl(2-oxocyclohexyl)sulfonium perfluorobutanesulfonate,
cyclohexylmethyl(2-oxocyclohexyl)sulfonium perfluorooctanesulfonate,
2-methyl-4,6-bis(trichloromethyl)-1, 3, 5-triazine,
2,4,6-tris(trichloromethyl)-1,3,5-triazine,
2-phenyl-4,6bis(trichloromethyl)-1,3,5-triazine,
2-(4-chlorophenyl)-4,6-bis(trichloromethyl)-1,3,5-triazine
2-(4-methoxyphenyl)-4,6-bis(trichloromethyl)-1,3,5-triazine,
2-(4-methoxy-1-naphthyl)-4,6-bis(trichloromethyl)-1,3,5-triazine,
2-(benzo[d][1,3]dioxolane-5-yl)-4,6-bis(trichloromethyl)-1,3,5-triazine,
2-(4-methoxystyryl)-4,6-bis(trichloromethyl)-1,3,5-triazine,
2-(3,4,5-trimethoxystyryl)-4,6-bis(trichloromethyl)-1,3,5-triazine,
2-(3,4-dimethoxystyryl)-4,6-bis(trichloromethyl)-1,3,5-triazine,
2-(2,4-dimethoxystyryl)-4,6-bis(trichloromethyl)-1,3,5-triazine,
2-(2-methoxystyryl)-4,6-bis(trichloromethyl)-1,3,5-triazine,
2-(4-butoxystyryl)-4,6-bis(trichloromethyl)-1,3,5-triazine,
2-(4-pentyloxystyryl)-4,6-bis(trichloromethyl)-1,3,5-triazine,
diphenyl disulfone,
di-p-tolyl disulfone,
bis(phenylsulfonyl)diazomethane,
bis(4-chlorophenylsulfonyl)diazomethane,
bis(p-tolylsulfonyl)diazomethane,
bis(4-tert-butylphenylsulfonyl)diazomethane,
bis(2,4-xylylsulfonyl)diazomethane,
bis (cyclohexylsulfonyl)diazomethane, (benzoyl)(phenylsulfonyl)diazomethane,
1-benzoyl-1-phenylmethyl p-toluenesulfonate (so-called benzointosylate),
2-benzoyl-2-hydroxy-2-phenylethyl p-toluenesulfonate (so-called xcex1-methylolbenzointosylate),
1,2,3-benzenetriyl trimethanesulfonate,
2,6-dinitrobenzyl p-toluenesulfonate,
2-nitrobenzyl p-toluenesulfonate,
4-nitrobenzyl p-toluenesulfonate,
N-(phenylsulfonyloxy)succinimide,
N-(trifluoromethylsulfonyloxy)succinimide,
N-(trifluoromethylsulfonyloxy)phthalimide,
N-(trifluoromethylsulfonyloxy)-5-norbornene-2,3-dicarboxyimide,
N-(trifluoromethylsulfonyloxy)naphthalimide,
N-(10-camphorsulfonyloxy)naphthalimide, and the like.
It is also known that, generally in a chemical amplifying type positive resist composition, performance deterioration due to the deactivation of an acid associated with leaving after exposure can be reduced by adding basic compounds, especially basic nitrogen-containing organic compounds such as amines as quenchers. It is also preferable in the present invention that such basic compounds are added. Concrete examples of the basic compounds to be used as quenchors include the ones represented by the following formulae: 
wherein R11, R12 and R17 represent, independently each other, hydrogen, cycloalkyl, aryl or alkyl which may be optionally substituted with a hydroxyl, amino which may be optionally substitiuted with alkyl having 1 to 6 carbon atoms, or alkoxy having 1 to 6 carbon atoms; R13, R14 and R15, which are same or different from each other, represent hydrogen, cycloalkyl, aryl, alkoxy or alkyl which may be optionally substituted with a hydroxyl, amino which may be optionally substituted with alkyl having 1 to 6 carbon atoms, or alkoxy having 1 to 6 carbon atoms; R16 represents cycloalkyl or alkyl which may be optionally substituted with a hydroxyl, amino which may be optionally substitiuted with alkyl having 1 to 6 carbon atoms, or alkoxy having 1 to 6 carbon atoms; A represents alkylene, carbonyl, imino, sulfide or disulfide. The alkyl represented by R11 to R17 and alkoxy represented by R13 to R15 may have about 1 to 6 carbon atoms. The cycloalkyl represented by R11 to R17 may have about 5 to 10 carbon atoms and the aryl represented by R11 to R15 and R17 may have about 6 to 10 carbon atoms. The alkylene represented by A may have about 2 to 6 carbon atoms and may be straight-chained or branched. The group represented by R11 to R17 may be straight chain or branched,
The resist composition of the present invention preferably contains the resin in an amount of 80 to 99.9% by weight, and the acid generating agent in an amount of 0.1 to 20% by weight based on the total weight of the resin and the acid generating agent. When a basic compound is used as a quencher, it is preferably contained in an amount in the range of 0.001 to 1 part by weight, more preferably 0.01 to 0.3 part by weight per 100 parts by weight of the resin. The composition may also contain, if required, a small amount of various additives such as sensitizers, dissolution inhibitors, resins other than the above resin, surfactants, stabilizers, and dyes so far as the objects of the present invention is not harmed.
The resist composition of the present invention generally becomes a resist solution in the state in which the above-described components are dissolved in a solvent to be applied on a substrate such as a silicon wafer.
The resist film applied on a substrate, and dried is subjected to an exposure treatment for patterning Then, after a heat-treatment for promoting a protecting deblocking reaction, development by an alkali developer is conducted. The alkali developer herein used can be various kinds of alkaline aqueous solutions used in this field. In general, an aqueous solution of tetramethylammoniumhydroxide or (2-hydroxyethyl)trimethylammoniumhydroxide (so-called colline) is often used.
The present invention will be described in more detail by way of examples, which should not be construed as limiting the scope of the present invention. All parts in examples are by weight unless otherwise stated. The weight-average molecular weight is a value determined from gel permeation chromatography using polystyrene as a reference standard.
In this specification, the monomers respectively having the following structures will be referred to, in the order from left to right of the structures, as xe2x80x9c5-methacryloyloxy-2,6-norbornancarbolactonexe2x80x9d, and xe2x80x9c5-acryloyloxy-2, 6-norbornancarbolactonexe2x80x9d. 